Apparatus and method for thermal compensation during additive manufacturing

ABSTRACT

An additive manufacturing apparatus includes an extruder and a gear pump in fluid communication with extruder. The additive manufacturing apparatus also includes a nozzle in fluid communication with the gear pump. The extruder is connected to a guide member such that at least a portion of the extruder is configured to expand and move along the guide member according to a thermal expansion of the extruder.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This patent application is a continuation of and claims the benefit ofpriority to U.S. patent application Ser. No. 16/596,089, filed on Oct.8, 2019, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

Aspects of the present disclosure relate to apparatus and methods forfabricating components. In some instances, aspects of the presentdisclosure relate to apparatus and methods for fabricating components(such as, e.g., automobile parts, medical devices, machine components,consumer products, etc.) via additive manufacturing techniques orprocesses, such as, e.g., 3D printing manufacturing techniques orprocesses.

BACKGROUND

Additive manufacturing techniques and processes generally involve thebuildup of one or more materials to make a net or near net shape (NNS)object, in contrast to subtractive manufacturing methods. Though“additive manufacturing” is an industry standard term (ASTM F2792),additive manufacturing encompasses various manufacturing and prototypingtechniques known under a variety of names, including, e.g., freeformfabrication, 3D printing, rapid prototyping/tooling, etc. Additivemanufacturing techniques may be used to fabricate simple or complexcomponents from a wide variety of materials. For example, a freestandingobject may be fabricated from a computer-aided design (CAD) model.

A particular type of additive manufacturing is commonly known as 3Dprinting. One such process, commonly referred to as Fused DepositionModeling (FDM) or Fused Layer Modeling (FLM) comprises a process ofmelting a thin layer of thermoplastic material, and applying thismaterial in layers to produce a final part. This is commonlyaccomplished by passing a continuous thin filament of thermoplasticmaterial through a heated nozzle, which melts the material and appliesit to the structure being printed. The heated material may be applied tothe existing structure in thin layers, melting and fusing with theexisting material to produce a solid finished product.

The filament used in the aforementioned process may be produced by, forexample, using a plastic extruder, which may include a steel extruderscrew configured to rotate inside of a heated steel barrel.Thermoplastic material in the form of small pellets may be introducedinto one end of the rotating screw. Friction from the rotating screw,combined with heat from the barrel may soften the plastic, which maythen be forced under pressure through a small round opening in a diethat is attached to the front of the extruder barrel. This extrudes astring of material which is cooled and coiled up for use in the 3Dprinter.

Melting a thin filament of material in order to 3D print an item may bea very slow process, which may be suitable for producing relativelysmall items or a limited number of items. The melted filament approachto 3D printing may be too slow to manufacture large items. However, thefundamental process of 3D printing using molten thermoplastic materialsmay offer advantages for the manufacture of larger parts or a largernumber of items.

In some instances, the process of 3D printing a part may involve atwo-step process. For example, the process may utilize a large printbead to achieve an accurate final size and shape. This two-step process,commonly referred to as near-net-shape, may begin by printing a part toa size slightly larger than needed, then machining, milling, or routingthe part to the final size and shape. The additional time required totrim the part to final size may be compensated for by the fasterprinting process.

Print heads for additive manufacturing machines used to printthermoplastic material in relatively large beads have generally includeda vertically-mounted extruder connected to a print nozzle to deposit thebead of material onto a surface and/or a part being printed. Thesetraditional print heads may include an oscillating plate surrounding thenozzle, the plate being configured to oscillate vertically to flattenthe bead of material against the surface or part on which the bead isdeposited.

The aforementioned traditional print heads may have several drawbacks.For example, the height of the print nozzle with respect to the carriermay change along on a z-axis due to the thermal expansion or contractionof one or more components of the print head in such traditional printheads. This potential drawback may be due to the vertical extruder beingrigidly mounted to the carrier. As the extruder heats up, it may expandalong the Z-axis. Similarly, expansion may cause the nozzle to move inposition with respect to the carrier in a direction along the z-axis.When materials having different temperatures (e.g., due to differentmelting points) are printed, the nozzle may move to different heights,therefore the nozzle height may not be at the same height for eachprint. These issues may introduce difficulties when creating programsfor printing as the location of the nozzle may be dependent on thethermal expansion and/or contraction of the extruder, which may besufficiently large to affect the printing process.

SUMMARY

Aspects of the present disclosure relate to, among other things, methodsand apparatus for fabricating components via additive manufacturing or3D printing techniques. Each of the aspects disclosed herein may includeone or more of the features described in connection with any of theother disclosed aspects. An exemplary object of the present disclosureis to control thermal expansion and/or contraction of a print head so aheight of a nozzle may remain at a fixed height with respect to thecarrier in a z-direction (vertical direction). In one aspect, anadditive manufacturing apparatus such as a computer numerical control(CNC) machine may include a melt pump mounted to the carrier to hold thenozzle in a an approximately fixed position while an expansion assemblyincluding, for example, the extruder, feed housing, transition housing,gearbox, and servomotor, may grow and/or shrink in the verticaldirection in accordance with the thermal expansion and/or contraction.In one aspect, movement of one or more components of the expansionassembly may be facilitated by a set of linear bearings and railsattached to the expansion assembly via the transition housing. Thus, asthe extruder and other components heat up and grow in length, thebearings may move up the rails via the linear bearings. The gear pumpmay be mounted to the carrier so the gear pump may be secured at a fixedposition relative to the carrier. In one aspect, the thermal expansionof these components does not affect the position of the gear pump or thenozzle. For example, a position of the nozzle may only by affected byits own thermal expansion. Such thermal expansion of the nozzle may beaddressed by using different length nozzle tips.

In one aspect, an additive manufacturing apparatus may include anextruder and a gear pump in fluid communication with the extruder, thegear pump supported on the additive manufacturing apparatus with theextruder. The additive manufacturing apparatus may also include a nozzlein fluid communication with the gear pump. The extruder may be movablyconnected to a guide member such that at least a portion of the extruderis configured to expand and move with respect to the guide memberaccording to a thermal expansion of the extruder.

In another aspect, an additive manufacturing apparatus may include anextruder supported on a support member and a gear pump fluidly coupledto the extruder. The additive manufacturing apparatus may also include anozzle in fluid communication with the gear pump and movable along anx-axis, a y-axis, and a z-axis to deposit a bead of thermoplasticmaterial. The extruder may be connected to a linear motion assembly onthe support member configured to raise and lower the extruder along thez-axis.

In another aspect, a method for thermal compensation during additivemanufacturing may include raising a temperature of an extruder from roomtemperature to an operating temperature and melting a thermoplasticmaterial with heat generated by at least one of an extruder and aplurality of heaters provided on the extruder. The method may alsoinclude receiving the melted thermoplastic material with a gear pumpdownstream of the extruder, and allowing the extruder to expand relativeto the nozzle due to an expansion of the extruder while raising thetemperature of the extruder.

In another aspect of the present disclosure, a print head may beconfigured to compensate for the thermal expansion and/or contraction.For example, a lead screw (e.g., ball screw or acme screw) mechanism maybe configured to raise and lower the transition housing and thecomponents attached thereto. For example, a lead screw (such as an acmescrew) mechanism may be configured to move within a top support bearing.As the extruder expands upward linearly, it may lift the lead screw. Inone aspect, the lead screw may be configured to slide upward in the topsupport bearing (e.g., by providing a lead screw with a reduced length).When the extruder cools down and contracts the lead screw may slidedownward in the top support bearing. Therefore, the extruder, feedhousing, transition housing, gearbox, and servomotor may be configuredto grow and shrink in a vertical direction in accordance with thethermal expansion of the components without the lead screw mechanismconstricting this motion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary aspects of the presentdisclosure and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 is a perspective view of an exemplary CNC machine operablepursuant to an additive manufacturing process to form articles or parts,according to an aspect of the present disclosure;

FIG. 2 is a perspective view of an exemplary carrier and extruderassembly of the exemplary CNC machine shown in FIG. 1;

FIG. 3 is an enlarged perspective view of an exemplary carrier andapplicator assembly of the exemplary CNC machine shown in FIG. 1;

FIG. 4 is an enlarged cutaway view of an exemplary applicator assemblyshown in FIG. 3;

FIG. 5 is a cross-section view of an exemplary high output print headassembly of the exemplary CNC machine shown in FIG. 1 from a first sideat a position of a rail and linear bearing of the CNC machine;

FIG. 6 is a cross-section view of an exemplary high output print headassembly of the exemplary CNC machine shown in FIG. 1 from a second sideopposite to the first side at a position of a lead screw mechanism ofthe CNC machine;

FIG. 7 is an enlarged front view of an exemplary low and hightemperature nozzle tips;

FIG. 8A is a perspective view of a machined lead screw device of the CNCmachine at ambient temperature; and

FIG. 8B is a perspective view of the machined lead screw device at anelevated temperature.

DETAILED DESCRIPTION

The present disclosure is drawn to, among other things, methods andapparatus for fabricating multiple components via additive manufacturingor 3D printing techniques. Specifically, the methods and apparatus mayinclude a print head configured to control thermal expansion orcontraction of the print head, which is configured to maintain a fixedor constant nozzle height with respect to a carrier (e.g., in adirection parallel to a z-axis). With reference to FIG. 1, an additivemanufacturing apparatus such as a computer numerical control (CNC)machine 1 may include a bed 20 provided with a pair of transverselyspaced side walls 21 and 22, a printing gantry 23 supported on sidewalls 21 and 22, and a trimming gantry 36 supported on side walls 21 and22. CNC machine 1 may also include a carriage 24 mounted on printinggantry 23, a support member or carrier 25 mounted on carriage 24, anextruder 61 mounted on carrier 25, and an applicator assembly orapplicator head 43 mounted on carrier 25. Carrier 25 may be formed byone or more plates that form a support structure for extruder 61 andapplicator head 43. A horizontal worktable 27 may be supported on bed 20between side walls 21 and 22. Horizontal worktable 27 may include asupport surface disposed in an x-y plane. Printing gantry 23 andtrimming gantry 36 may each be disposed so as to extend along a y-axis,and may each be supported by side walls 21 and 22. Printing gantry 23and trimming gantry 36 may be fixedly supported with respect to anx-axis by a set of guide rails 28 and 29 provided on the upper ends ofside walls 21 and 22. The printing gantry 23 and trimming gantry 36 maybe displaceable by a set of servomotors mounted on the printing gantry23 and trimming gantry 36 and operatively connected to tracks providedon the side walls 21 and 22 of the bed 20. Carriage 24 may be supportedon printing gantry 23 and provided with a support member 30 mounted onand displaceable along one or more guide rails, such as guide rails 31,32, and 33, which may be provided on the printing gantry 23. Carriage 24may be displaceable along the y-axis via guide rails 31, 32, and 33 by aservomotor mounted on the printing gantry 23 and operatively connectedto support member 30. Carrier 25 may be mounted on a set of spaced,vertically-extending guide rails 34 and 35 supported on the carriage 24for displacement of the carrier 25 relative to the carriage 24 along az-axis. Carrier 25 may be displaceable along the z-axis by a servomotormounted on the carriage 24 and operatively connected to the carrier 25.

As shown in FIG. 2, extruder 61 may be movably mounted to carrier 25 viaa pair of guide members or rails 44 and 45. Extruder 61 may be connectedto rails 44 and 45 by one or more bushings (see bearing 50 in FIG. 5).Extruder 61 may be driven by a servomotor 38 and a gearbox 39, which maybe attached to transition housing 37. In an exemplary embodiment, leadscrew 85, support bearing 86, and nut 87 (described below), may form anexemplary linear motion assembly. This linear motion assembly may alsoinclude rails 44 and 45. Extruder 61 may receive thermoplastic pelletsthrough a feed housing 40. The thermoplastic pellets may be transferred,via an extruder screw, through the barrel 42 where the pellets may bemelted by the friction of the screw and/or heat generated by heaters 41.Extruder 61 may then cause molten thermoplastic material to flow to agear pump 62 fluidly coupled to extruder 61 (FIG. 3).

As shown in FIG. 3, a gear pump (or melt pump) 62 may be fixedly mountedto the bottom of carrier 25 and may be supported on CNC machine 1 withextruder 61 via carrier 25. In an exemplary configuration, gear pump 62may be a positive displacement gear pump driven by a servomotor 63through a gearbox 64. Gear pump 62 may receive molten thermoplastic fromextruder 61 (FIG. 2), and meter out precise amounts of the moltenthermoplastic material at predetermined flow rates to nozzle 51 to printthe part by moving the nozzle along the x-axis, y-axis, and z-axis. Theextruder 61 and gear pump 62 together may provide the ability to utilizeextruder screw configurations which may cause uneven flow inconfigurations where only an extruder is provided. In one aspect, themelt pump may act to even out material flow and provide increased designfreedom for the extrusion screw.

A bead shaping roller 59, rotationally mounted in carrier bracket 47,may provide a means for flattening and leveling an oversized bead offluid material (e.g., molten thermoplastic material) extruded by thenozzle 51. Carrier bracket 47 may be adapted to be rotationallydisplaced by a servomotor 60. For example, servomotor 60 may be operablyconnected to carrier bracket 47 by a pulley 56 and belt 65.

With reference to FIG. 4, applicator head 43 may include a housing 46with a rotary union mounted therein. Pulley 56 may be machined into aninner hub 76 of the rotary union. The inner hub 76 may have an openingwith a diameter sized to receive the heated print nozzle 51. The innerhub 76 may rotate on a set of bearings 49 provided in an outer housing75 of the rotary union. The compression roller assembly may be attachedto the inner hub 76 of the rotary union so that the compression roller59 rotates about the print nozzle 51. The rotary union may also containbarb fittings 67 and 68 in fluid communication with coolant passages 70.In one aspect, coolant passages 70 may surround the inner hub 76 and theinside of the outer housing 75 of the rotary union. The coolant passages70 continue through quick disconnect fittings 72 into the axle 73 of thecompression roller 59.

As shown in FIGS. 3 and 4, for example, an oversized bead of flowablematerial (e.g., molten thermoplastic) may be provided under pressurefrom a source disposed on carrier 25 (e.g., gear pump 62) or anothersource, to applicator head 43. This material may be provided to a nozzle51 in communication with applicator head 43, which may be fixedlyconnected to carrier 25. In use, the flowable material 53 (e.g.,thermoplastic material) may be heated sufficiently to form a moltenbead, which is then extruded through applicator nozzle 51 to formsubstantially uniform, smooth rows of deposited material on a surface ofworktable 27. Such beads of molten material may be flattened, leveled,and/or or fused to adjoining layers with substantially no trapped air bybead-shaping compression roller 59 with the layers forming 3D printedproducts.

As shown in FIG. 5, the gear pump 62 may be fixedly attached to thebottom of the carrier 25. The extruder 61, feed housing 40, transitionhousing 37, gearbox 39, and servomotor 38 may together form a group ofcomponents that expand as a unit. These expanding components, which maybe referred to as an expansion unit or expansion assembly, may each beconnected at positions above gear pump 62 along the z-axis, and may beconfigured to move (via expansion) vertically along linear rails (e.g.,substantially trapezoidal rectangular, or cylindrical shafts) 44 and 45.One or more of the extruder 61, feed housing 40, transition housing 37,gearbox 39 or servomotor 38 may form an exemplary heated component that,when heated, is configured to move away from gear pump 62 and away fromnozzle 51 in direction 80, for example. One or more bushings or linearbearings 50 may be provided on rails 44 and 45 and may be attached to arear surface of transition housing 37. In one aspect, shafts 44 and 45and linear bearings 50 may operate as guides to facilitate verticalmotion of these components of print head 99. In this manner, as thelength of the expansion assembly increases with a corresponding increasein temperature during operation of machine 1, a change in dimension mayoccur at the top of the expansion assembly. However, as the gear pump 62may be fixed to the carrier 25, gear pump 62 and nozzle 51 may remainfixed at positions below the expansion assembly and are not affected bythe expansion of the expansion assembly. This may provide the ability tomaintain the vertical height of the print nozzle 51 approximatelyconstant, as the expansion of the expansion assembly may not affect theposition of gear pump 62 and nozzle 51. Additionally, as the expansionassembly increases in temperature, the components of the expansionassembly may grow in length, which may cause linear bearing 50 togradually move up rails 44 and 45. At least a portion of extruder 61,for example, may be configured to move along rails 44 and 45 via slidingmotion of linear bearings 50 along direction 80. In one aspect, nozzle51 may acquire thermal expansion by a heat of thermoplastic materialtherein and may expand itself. The direction of the expansion of nozzle51 may correspond to direction 82, which is approximately opposite todirection 80, as shown in FIG. 5.

The increase in temperature may include raising a temperature ofextruder 61 from room temperature to an operating temperature (e.g., atemperature experienced by extruder 61 when material within the extruder61 is melted). This temperature may be generated by at least a screw ofextruder 61 and/or heaters 41. Gear pump 62 may receive this materialwhile remaining at a fixed position relative to carrier 25 as pump 62may be fastened directly to carrier 25. A length of extruder 61, as wellas an overall length of the expansion assembly, may increase alongdirection 80 due to the expansion of the expansion assembly (includingextruder 61) as the temperature of these components increases to anoperating temperature. The operating temperature of each of thecomponents of the expansion assembly may not necessarily be the sametemperature.

Print head 99 may include a lead screw 85 as shown in FIGS. 2, 6, 8A,and 8B. Lead screw 85 may be a threaded screw, such as an acme screw,and may be configured to allow transition housing 37 and the othercomponents of the expansion assembly to rise and descend on rails 44 and45. In an alternate configuration, a ball screw may be employed in placeof a lead screw. For example, lead screw 85 may be rotated by aservomotor (not shown) to raise and lower one or more components of theexpansion assembly. In an exemplary configuration, the transitionhousing 37 may be raised or lowered to facilitate replacement ofextruder screws and/or melt cores, for example, by separating transitionhousing 37 from extruder 61 and rotating lead screw 85. A nut 87 may befixedly mounted to the back of the transition housing 37 to facilitatethe motion of transition housing 37 along lead screw 85. When lead screw85 is provided as an acme screw, nut 87 may be provided as an acme nut.Similarly, nut 87 may be formed as a ball nut when a ball screw isprovided in place of a lead screw.

As best shown in FIGS. 8A and 8B, lead screw 85 may extend within a topsupport bearing 86 that may operate with lead screw 85 to compensate forthe thermal expansion and contraction of the extruder 61 and othercomponents. For example, a length (and/or diameter) of the screw 85 maybe reduced by a predetermined amount. As illustrated in FIGS. 8A and 8B,a portion of screw 85 may have a diameter that is reduced in comparisonto the remainder of screw 85 by a suitable machining process, such asturning, forming a machined portion 90. The reduction in the diameter,of screw 85 may allow the screw 85 to move vertically within, and withrespect to, the top support bearing 86. In one aspect, portion 90 oflead screw 85 may be reduced in diameter such that expansion of the leadscrew does not excessively constrict nut 87. For example, as shown inFIG. 8A, lead screw 85 may include machined portion 90 at an end portionthereof. This reduced diameter may be achieved, for example, by reducinga diameter of threading present on the lead screw 85. In one aspect,this threading, which may form an outer (maximum) diameter of lead screw85, may be partially removed from lead screw 85 at machined portion 90.If desired, an entirety of the threading may be machined away in portion90, resulting in a substantially uniform cylindrical surface. Forclarity, individual threads are not shown in FIGS. 8A and 8B.

FIG. 8A illustrates an exemplary position of lead screw 85, includingmachined portion 90 extending through top support bearing 86, when CNCmachine 1 is at an approximately ambient or room temperature environment(e.g., at a temperature of between about 65 and 85 degrees Celsius). Asthe extruder 61 and/or the other components of the expansion assemblygenerate and/or receive heat and expand, such expansion may cause leadscrew 85 to move in an upward direction.

For example, the lead screw 85 may advance (expand vertically) from theexemplary position illustrated in FIG. 8A to the exemplary positionshown in FIG. 8B. In one aspect, FIG. 8B may correspond to a maximumtemperature of extruder 61 and the other components of CNC machine 1.During this motion, the lead screw 85, and, in particular, machinedportion 90, may be configured to slide upward in the top support bearing86 by an amount that is at least as large as an amount of motion causedby the thermal expansion. When the extruder 61 cools down and contracts,machined portion 90 of lead screw 85 may move in an opposite direction,sliding downward in the top support bearing 86. Support bearing 86 maypermit vertical (linear) expansion and movement of lead screw 85, whileproviding radial support to screw 85. In one aspect, support bearing 86may remain in a fixed position on carrier 25, while lead screw 85 moveswith respect to both support bearing 86 and carrier 25. Therefore, theexpansion assembly formed by extruder 61, feed housing 40, transitionhousing 37, gearbox 39, and servomotor 38, may grow and shrink in anapproximately vertical direction due to the thermal expansion of itsconstituent components without being constricted by the lead screwmechanism.

To facilitate maintenance, such as replacement of an extruder screwwithin extruder 61, lead screw 85 may be manually rotated (e.g., in aclockwise direction), to lower screw 85 and cause the washer and nut(s)(as shown at the top of lead screw 85 in FIGS. 8A and 8B), to contactthe top end of bearing 86. This action may be performed at ambienttemperature, or at an elevated temperature, if desired. Lowering screw85 in the manner, while transition housing 37 is separated from extruder61, may increase the distance between transition housing 37 and extruder61 (see FIG. 2) by moving extruder 61 downward. Moreover, transitionhousing 37, which may be slidably mounted on rails 44 and 45 (see FIG.5), may be raised to further increase the distance between extruder 61and transition housing 37 while extruder 61 remains secured via nut 87(see FIG. 6). Transition housing 37 then may be rotated away fromextruder 61, providing access to the top of extruder 61. Oncemaintenance is complete, lead screw 85 may be returned to the positonshown in FIG. 8A.

As the position of nozzle 51 may be affected by the expansion of nozzle51 itself, and not the expansion of the expansion assembly, it may bepossible to compensate for the thermal expansion of the nozzle 51 byusing different lengths of nozzles tips for different materials havingdifferent melting points. FIG. 7 shows two exemplary nozzles 51A and 51Bthat may be employed as nozzle 51. A first nozzle 51A may be configuredfor use with a lower temperature material. A second nozzle 51B may beconfigured for use with a material that is used at a higher temperature(e.g., has a higher melting point) as compared to the first material.Thus, second nozzle 51B may have a slightly shorter nozzle tip ascompared to first nozzle 51A to account for the increased thermalexpansion that second nozzle 51B may experience. Nozzle 51B may includea groove or any other suitable feature to facilitate identificationbetween nozzle 51A, for example. Thus, nozzles 51A and 51B may bereadily differentiated, and may have a marking, such as a groove,associated with a particular temperature and/or a particular material.For example, nozzle 51A may be associated with a first thermoplasticmaterial having a first melting point, while nozzle 51B may beassociated with a second thermoplastic material having a second meltingpoint that is larger than the first melting point. The groove, or otheridentification, on nozzle 51B, may be associated with the secondthermoplastic material and/or the second melting point. Additionally,the use of a groove may facilitate identification of a nozzle 51A, 51B,that is currently installed in applicator head 43. Thus, the exemplarygroove may allow identification of nozzle 51B without the need to employa measurement device.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations and modifications of the presentinvention which come within the province of those persons havingordinary skill in the art to which the aforementioned inventionpertains. However, it is intended that all such variations not departingfrom the spirit of the invention be considered as within the scopethereof as limited by the appended claims.

What is claimed is:
 1. A method for additive manufacturing using anadditive manufacturing apparatus including an extruder, a gear pump, anda nozzle, the method comprising: heating the extruder to an operatingtemperature; melting a thermoplastic material in the extruder; receivingthe melted thermoplastic material with the gear pump downstream of theextruder; and allowing the extruder to expand relative to the nozzle dueto an expansion of the extruder as a result of the heat, wherein, whilethe extruder is allowed to expand, the gear pump is secured to a fixedposition on a carrier that carries the extruder and the gear pump. 2.The method of claim 1, wherein the additive manufacturing apparatusincludes a support member on which the gear pump is fixed, and wherein aposition of the gear pump is maintained constant with respect to thesupport member.
 3. The method of claim 1, wherein raising thetemperature of the extruder causes the extruder to expand in a directionaway from the nozzle.
 4. The method of claim 3, further including:raising a temperature of the nozzle; and allowing the nozzle to expandrelative to the gear pump and away from the extruder.
 5. The method ofclaim 1, wherein heating the extruder includes generating heat by theextruder to melt the thermoplastic material, the heat causing theextruder to expand and, due at least in part to this expansion, movewith respect to a guide member of the additive manufacturing apparatus.6. The method of claim 5, wherein the guide member is a rail secured toa carriage, the carriage being secured to and moveable with a gantry ofthe additive manufacturing apparatus.
 7. The method of claim 5, furtherincluding translating a transition housing that is configured to beconnected to the extruder with respect to the guide member, by rotatinga lead screw of a linear motion assembly.
 8. The method of claim 1wherein, while the extruder is allowed to expand, a lead screw of alinear motion assembly, for positioning the nozzle, is allowed toexpand.
 9. The method of claim 8, wherein the extruder is allowed toexpand in an upward direction away from the nozzle, and wherein the leadscrew is allowed to expand in the upward direction.
 10. An additivemanufacturing method, comprising: heating a thermoplastic materialwithin an extruder of an additive manufacturing apparatus; receiving thethermoplastic material with a gear pump downstream of the extruder;providing the thermoplastic material to a nozzle of the additivemanufacturing apparatus via the gear pump; moving the nozzle of theadditive manufacturing apparatus to deposit the thermoplastic material;and allowing a portion of a vertical motion assembly to expand in avertical direction such that the portion of the vertical motion assemblymoves away from the nozzle, wherein, while the vertical motion assemblyis allowed to expand, the gear pump is secured to a fixed position on acarrier that carries the extruder and the gear pump.
 11. The method ofclaim 10, wherein the additive manufacturing apparatus includes asupport member on which the gear pump is fixed, and wherein a positionof the gear pump is maintained constant with respect to the supportmember while the thermoplastic material is provided to the nozzle. 12.The method of claim 10, further including raising a temperature of theextruder, by heating the thermoplastic material, causing the extruder toexpand away from the nozzle.
 13. The method of claim 12, wherein thevertical direction is an upward direction, the method further including:raising a temperature of the nozzle by providing the thermoplasticmaterial to the nozzle; and allowing the nozzle to expand relative tothe gear pump and move in a downward direction.
 14. The method of claim10, further including heating the extruder and causing the extruder toexpand such that the extruder moves according to this expansion withrespect to a guide member of the vertical motion assembly.
 15. Themethod of claim 14, wherein the guide member is a rail secured to acarriage, the carriage being secured to and moveable with ahorizontally-moveable gantry of the additive manufacturing apparatus.16. The method of claim 14, further including translating a transitionhousing that is configured to be connected to the extruder with respectto the guide member, by rotating a lead screw of the vertical motionassembly.
 17. The method of claim 10 wherein, while the extruder isallowed to expand, a lead screw of the vertical motion assembly, forpositioning the nozzle, is allowed to expand.
 18. The method of claim17, wherein the extruder is allowed to expand in an upward directionaway from the nozzle, and wherein the lead screw is allowed to expand inthe upward direction.